Performance Tuning 101: Parallelism

Performance Tuning 101: Parallelism
Robert L Davis Database Engineer @SQLSoldier Performance Tuning 101: Parallelism

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Robert L Davis @SQLSoldier PASS Security Virtual Chapter
Microsoft Certified Master Data Platform MVP @SQLSoldier Database Engineer BlueMountain Capital Management 17+ years working with SQL Server PASS Security Virtual Chapter Volunteers needed Database Engineer at BlueMountain Capital Management Foremer Principal Database Architect at DB Best Technologies Former Principal DBA at Outerwall, Inc Former Sr. Product Consultant with Idera Software Former Program Manager for SQL Server Certified Master program in Microsoft Learning Former Sr. Production DBA / Operations Engineer at Microsoft (CSS) Microsoft Certified Master: SQL Server 2008 / MCSM Charter: Data Platform Co-founder of the SQL PASS Security Virtual Chapter MCITP: Database Developer: SQL Server 2005 and 2008 MCITP: Database Administrator: SQL Server 2005 and 2008 MCSE: Data Platform MVP 2014 Co-author of Pro SQL Server 2008 Mirroring Former Idera ACE (Advisors & Community Educators) 2 time host of T-SQL Tuesday Guest Professor at SQL University, summer 2010, spring/summer 2011 Speaker at SQL PASS Summit 2010, 2011, and 2012 including a pre-con in 2012 Speaker/Pre-con at SQLRally 2012 17+ years working with SQL Server Writer for SQL Server Pro (formerly SQL Server Magazine) Member: Mensa Dog picture: Maggie and Woody SQLCruise instructor: Seattle to Alaska 2012 Speaker at SQL Server Intelligence Conference in Seattle 2012 Blog: Twitter:

Parallelism: Architecture

Parallelism: Architecture Max Worker Threads = 576 for 8 logical CPUs = 72/scheduler

Parallelism: Architecture

SQL will generally keep all threads on the same NUMA node

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes Local memory access faster than foreign memory access

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes Local memory access faster than foreign memory access Old NUMA (before Nehalem):

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes Local memory access faster than foreign memory access Old NUMA (before Nehalem): Foreign memory request sent to other node’s CPU for processing

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes Local memory access faster than foreign memory access Old NUMA (before Nehalem): Foreign memory request sent to other node’s CPU for processing Current NUMA (after Nehalem):

SQL will generally keep all threads on the same NUMA node If node is overloaded and other node is not, it may choose to span nodes Memory partitioned per NUMA node though accessible to all nodes Local memory access faster than foreign memory access Old NUMA (before Nehalem): Foreign memory request sent to other node’s CPU for processing Current NUMA (after Nehalem): Foreign memory request sent directly to other node’s memory

Max Degree of Parallelism

Max Degree of Parallelism Server configuration starting point:

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0 >8 CPUs: 8

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0 >8 CPUs: 8 NUMA: Lesser of number of CPUs per node or 8

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0 >8 CPUs: 8 NUMA: Lesser of number of CPUs per node or 8 Can be over-ridden by MaxDOP query hint

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0 >8 CPUs: 8 NUMA: Lesser of number of CPUs per node or 8 Can be over-ridden by MaxDOP query hint Both over-ridden by Resource Governor (RG)

Max Degree of Parallelism Server configuration starting point: 8 or less CPUs: leave at 0 >8 CPUs: 8 NUMA: Lesser of number of CPUs per node or 8 Can be over-ridden by MaxDOP query hint Both over-ridden by Resource Governor (RG) Will use the lesser of MaxDOP or RG if both defined

Max DOP: What will it use exactly? Query Hint (QH) Resource Governor (RG) Server Config Effective MAXDOP of query Not set Not set (0) Server decides (up to 64) Set Use server config Use RG Use QH Use min(RG, QH) Use min (RG, QH) Adapted from by Jack Li

Cost Threshold for Parallelism

Cost Threshold for Parallelism All operations in an execution plan have an estimated cost value

Cost Threshold for Parallelism All operations in an execution plan have an estimated cost value Based loosely on the CPU ticks of a long-forgotten developer’s desktop who worked on the feature

Cost Threshold for Parallelism All operations in an execution plan have an estimated cost value Based loosely on the CPU ticks of a long-forgotten developer’s desktop who worked on the feature Used by the query optimizer to determine if a task is a candidate for parallelization

Cost Threshold for Parallelism All operations in an execution plan have an estimated cost value Based loosely on the CPU ticks of a long-forgotten developer’s desktop who worked on the feature Used by the query optimizer to determine if a task is a candidate for parallelization Increase setting to cause smaller plans to not parallelize but still allow bigger plans to use parallelism

Parallelism can be stripped out at run-time if server is short of memory or threads

Parallelism can be stripped out at run-time if server is short of memory or threads If cost for a serial plan is above the cost threshold for parallelism, a parallel plan will be generated, but SQL Server will use the lower total costing plan

Parallelism can be stripped out at run-time if server is short of memory or threads If cost for a serial plan is above the cost threshold for parallelism, a parallel plan will be generated, but SQL Server will use the lower total costing plan Will choose the serial plan if cost of parallel plan is higher

Demo

Fixing CXPacket Waits

Fixing CXPacket Waits Communication eXchange Packet

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken Often indicative of query tuning opportunities

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken Often indicative of query tuning opportunities Over-parallelization can cause excessive waits

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken Often indicative of query tuning opportunities Over-parallelization can cause excessive waits Beware advice to set Max Degree of Parallelism to 1

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken Often indicative of query tuning opportunities Over-parallelization can cause excessive waits Beware advice to set Max Degree of Parallelism to 1 Only useful in very rare edge case

Fixing CXPacket Waits Communication eXchange Packet CXPacket waits are not what’s broken Often indicative of query tuning opportunities Over-parallelization can cause excessive waits Beware advice to set Max Degree of Parallelism to 1 Only useful in very rare edge case Goal most of the time is to find the right balance between execution speed and concurrency

The little yellow circle with double arrows means it was compiled as a parallel operation

The little yellow circle with double arrows means it was compiled as a parallel operation The thicker the arrow between icons, the more work was done

The little yellow circle with double arrows means it was compiled as a parallel operation The thicker the arrow between icons, the more work was done Properties tab can show you stats per thread for the highlighted icon or arrow

The little yellow circle with double arrows means it was compiled as a parallel operation The thicker the arrow between icons, the more work was done Properties tab can show you stats per thread for the highlighted icon or arrow Thread 0 will always show 0 rows as it is the watcher thread

The database engine still has the option to run with less threads or in serial even if compiled as a parallel operation

The database engine still has the option to run with less threads or in serial even if compiled as a parallel operation Plan details will still show the number of threads from the compiled plan but will only show 0 for all threads not used

Which operation did the most work?

Which operation did the most work? Look at the threads in the plan details

What is the Parallelism (Repartition Streams) operator doing?

What is the Parallelism (Repartition Streams) operator doing? Plan details shows it redistributes the rows more evenly

Q & A

Thank you for attending!
¡Gracias! Thank you for attending! My blog: Twitter: twitter.com/SQLSoldier

Performance Tuning 101: Parallelism

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